Fix (sometimes serious) performance problem on submitting profiles for specified contacts

[eileenmcnaughton]

Overview

Prevents unnecessary soul-destroying & sometimes server-destroying queries when submitting a profile for a known contact id

Before

Despite the contact id being known ($form->_id) and ultimately used the code does expensive queries to retrieve possible duplicates (before discarding that information). When using a profile block with only tags in it with contactlayouteditor this creates a query that makes strong servers cry

After

Unnecessary queries not run

Technical Details

$form->_id is set when the contact id is known - e.g in edit, in contactlayouteditor profile
blocks. However, current logic still retrieves duplicates and then... does nothing
with them if ->_id is set. By moving the if up higher we can save the server from
doing unnecesary queries. Note that if you submit a tag profile with no other fields in it
the query is server-destroyingly bad with this

Comments

@colemanw here is the fix to civicrm/org.civicrm.contactlayout#46 following up on the preliminary refactor you reviewed.

[civibot]

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[colemanw]

Looks great. Bonus points for snarky code comments.